海洋に産する鉄‐マンガン団塊およびクラストの化学組成 ２ 希土類元素，酸化されやすい元素および酸素酸元素

Abstract

The REE contents increase in the following sequence : hydrothermal crusts ≤ suboxic-diagenetic nodules < oxic-diagenetic nodules < hydrogenetic crusts. With the above order, a positive Ce anomaly and a Sm maximum when normalized to deep-sea water become remarkable. These phenomena are controlled by kinetics rather than by REE concentrations in the environments where nodules and crusts are precipitated. The Sm maximum is explained by the competition between REE adsorption on oxides and REE stabilization by their complexation with ligands in seawater. The contents of readily oxidized elements such as Co, Pb, Ce and Pt in nodules and crusts decrease with increasing water depth. Their contents are also controlled by kinetics rather than by their concentrations and redox potentials in the depositing environments. The contents of oxyanionic elements are not so varied among nodules and crusts of different origins in comparison with those of cationic elements. This phenomenon is attributed to the adsorption of oxyanions on oxides without their substitution for the elements forming the oxides, because molecules of oxyanions are large. The adsorption is a rapid process relative to the substitution.